1. Field of the Invention
The present invention relates generally to machine tools, and more specifically to tool changers for machine tools.
2. Discussion of Related Art
Typically, tool changing systems are used in modem program-controlled machine tools. They serve to transfer tools between a tool magazine and the vertical or horizontal work spindle of the machine tool. Certain components of the tool changers, including their tong-shaped grippers, move on predefined tracks to receive the selected tools in predetermined changing positions. Using their tongs, the grippers can laterally grip a ring groove on the tool taper when the tool is located at the changing position of the magazine. The tool is taken out of the magazine by a pull-off movement. The tool is brought into a position where a rotary or swiveling motion of the tool changer may effect the exchange of the tool into the work spindle. The changing process of a “used” tool from the work spindle to an open space in the tool magazine is carried out in reverse functional sequence.
German patent publication DE 35 31 160 A1 describes a tool changer for a machine tool. The gripper approaches the flange of a tool taper laterally with two legs that are movable in opposite directions. The legs can be locked by means of a device after surrounding the tool taper. This protects the tool taper in the gripper from being pulled out. A connecting link provided on the machine tool pushes the locking element axially out of the flange's range on the tool taper when the gripper is moved in front of the tool holding fixture.
German patent publication DE 42 15 697 A1 describes another tool changer for machine tools. The gripper of this device is arranged on a changer arm movably formed between the tool magazine and the tool receiving position of the work spindle. The changer arm carries two grippers arranged side by side, which in their initial position are disposed parallel to the axis of a spindle for holding tools. The two grippers are connected to the changer arm by a swivel device and can be shifted synchronously in parallel and relative to the spindle axis in the direction of a connecting line between both grippers.
Furthermore, German patent publication DE 37 17 201 A1 describes a gripper for tools of a machine tool, where two movable jaws provide for positive engagement with the groove of a tool taper. In order for the gripper legs to positively engage the groove on the thickened end of the tool taper, the gripper is provided with a movable operating element. This element moves the legs to an expanded position for introducing the tool taper, and to a closed position for positively gripping the tool taper. This operating element is operated by a stationary stop of the machine tool. Furthermore, the gripper has two fixed jaws arranged co-axially with the two gripper legs. The jaws project beyond the ends of the gripper legs. Both jaws gradually merge into a common semi-circular holding fixture where a centering groove is formed. However, the use of movable gripper legs and additional fastened jaws for each gripper is technically expensive and offers risk of malfunction.
In modern milling and boring centers for the industrial scale manufacture of tools, the essential operating times with a single tool are often within a range of seconds. Tool changing after each machining process takes a few seconds. This results in a relatively unfavorable ratio between the total operating time and the time required for the corresponding tool changing. The production yield of the machine is thereby affected. This ratio of chip-to-chip and operating time becomes even more unfavorable if heavy-duty spindles, for example high speed spindles, are used where the objective is achieving high chip production.